U.S. patent application number 13/632521 was filed with the patent office on 2013-01-31 for method for operating a delivery unit for a reducing agent and motor vehicle having a delivery unit.
This patent application is currently assigned to EMITEC GESELLSCHAFT FUER EMISSIONSTECHNOLOGIE MBH. The applicant listed for this patent is EMITEC GESELLSCHAFT FUER EMISSIONSTECHNOLOGIE MBH. Invention is credited to PETER BAUER, JAN HODGSON.
Application Number | 20130025268 13/632521 |
Document ID | / |
Family ID | 44123324 |
Filed Date | 2013-01-31 |
United States Patent
Application |
20130025268 |
Kind Code |
A1 |
BAUER; PETER ; et
al. |
January 31, 2013 |
METHOD FOR OPERATING A DELIVERY UNIT FOR A REDUCING AGENT AND MOTOR
VEHICLE HAVING A DELIVERY UNIT
Abstract
A method for operating a reducing agent delivery unit having a
tank, a feed line running from the tank to an addition point, a
return line branching off from the feed line and a valve to be
activated with an electrical current for closing off the return
line, includes initially applying an activation current to the
valve for a first time interval. Subsequently, a holding current is
applied to the valve when the first time interval has elapsed.
Then, an operating variable of the delivery unit is determined and
at least the activation current, the holding current and/or the
first time interval are adapted as a function of the determined
operating variable. A motor vehicle having a delivery unit is also
provided.
Inventors: |
BAUER; PETER; (IMMENREUTH,
DE) ; HODGSON; JAN; (TROISDORF, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
EMISSIONSTECHNOLOGIE MBH; EMITEC GESELLSCHAFT FUER |
LOHMAR |
|
DE |
|
|
Assignee: |
EMITEC GESELLSCHAFT FUER
EMISSIONSTECHNOLOGIE MBH
LOHMAR
DE
|
Family ID: |
44123324 |
Appl. No.: |
13/632521 |
Filed: |
October 1, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2011/054311 |
Mar 22, 2011 |
|
|
|
13632521 |
|
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Current U.S.
Class: |
60/317 ;
137/1 |
Current CPC
Class: |
F01N 2900/1808 20130101;
F01N 2610/1466 20130101; Y02T 10/24 20130101; F01N 2900/0422
20130101; F01N 2610/1473 20130101; F01N 2900/1822 20130101; F01N
2900/1811 20130101; Y02A 50/2325 20180101; F01N 2610/02 20130101;
Y10T 137/0318 20150401; Y02A 50/20 20180101; Y02T 10/12 20130101;
F01N 3/208 20130101 |
Class at
Publication: |
60/317 ;
137/1 |
International
Class: |
F01N 3/02 20060101
F01N003/02; F17D 3/00 20060101 F17D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2010 |
DE |
10 2010 013 695.6 |
Claims
1. A method for operating a delivery unit for delivering a reducing
agent to an addition point, the method comprises the following
steps: providing the delivery unit with a tank, a feed line running
from the tank to the addition point, a return line branching off
from the feed line and a valve configured to be activated with an
electrical current for switching over the return line; a) applying
an activation current to the valve for a first time interval; b)
applying a holding current to the valve when the first time
interval has elapsed; c) determining an operating variable of the
delivery unit; and d) adapting at least one of the following
variables as a function of the determined operating variable: the
activation current; the holding current; or the first time
interval.
2. The method according to claim 1, which further comprises moving
a movable armature of the valve from an initial position into an
activated position with the activation current and holding the
movable armature in the activated position with the holding
current.
3. The method according to claim 1, which further comprises
providing the valve with a movable armature, a spring and an
exciter coil, and moving the movable armature with the exciter coil
counter to a spring force of the spring.
4. The method according to claim 1, which further comprises:
carrying out step c) at least as a function of the determined
operating variable of the delivery unit by including in the
operating variable at least one of the following parameters: a
pressure of the reducing agent in the delivery unit; a delivery
rate of a delivery pump associated with the delivery unit; a
characteristic current profile of a delivery pump associated with
the delivery unit; a leakage from the delivery unit; a temperature
of the reducing agent in the delivery unit; or a temperature of a
component in the delivery unit.
5. The method according to claim 1, which further comprises
carrying out the method repeatedly and carrying out an adaptation
of at least one of the following variables to an aging-induced
change of the valve: the activation current; the holding current;
or the first time interval.
6. The method according to claim 1, which further comprises
carrying out the method upon an initial start-up of the delivery
unit, and carrying out an adaptation of at least one of the
following variables to individual characteristics of the valve
resulting from production tolerances: the activation current; the
holding current; or the first time interval.
7. The method according to claim 1, which further comprises:
reducing the holding current in step b) to such an extent that
leakage from the delivery unit is detected in step c); and then
setting the holding current in step d) so as to be higher by a
predefined interval than the holding current reduced in step
b).
8. The method according to claim 1, which further comprises
generating the activation current and the holding current from a
system voltage using a pulse width manipulation.
9. The method according to claim 1, which further comprises
connecting a free-wheeling diode in parallel with the activatable
valve, and carrying out a deactivation of the holding current after
step d).
10. A motor vehicle, comprising: an internal combustion engine; an
exhaust system configured to purify exhaust gases of the internal
combustion engine, said exhaust system having an addition point;
and a delivery unit having a tank, a feed line running from said
tank to said addition point, a return line branching off from said
feed line, a valve to be activated with an electrical current for
closing off said return line, and a controller configured to
operate said delivery unit in accordance with the method of claim
1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation, under 35 U.S.C. .sctn.120, of
copending International Application No. PCT/EP2011/054311, filed
Mar. 22, 2011, which designated the United States; this application
also claims the priority, under 35 U.S.C. .sctn.119, of German
Patent Application DE 10 2010 013 695.6, filed Apr. 1, 2010; the
prior applications are herewith incorporated by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method for operating a delivery
unit for reducing agent. A delivery unit suitable for this purpose
has a feed line, which runs from a tank to an addition point (for
example at an exhaust line of a motor vehicle) and a return line
which branches off from the feed line, back into the tank. The
return line may generally be opened and/or closed off by a valve
which can be activated with an electrical voltage, in such a way
that a flow of reducing agent from the feed line to the return line
can be interrupted or prevented or produced in a targeted manner.
The invention also relates to a motor vehicle having a delivery
unit.
[0004] Such delivery units or dosing units may be used, for
example, together with devices for the purification of the exhaust
gases of internal combustion engines. In particular, such delivery
units are used in exhaust-gas treatment devices which are suitable
for selective catalytic reduction [SCR]. It is possible, with
selective catalytic reduction, for nitrogen oxide compounds
(NO.sub.x) in the exhaust gas to be reduced in an effective manner.
A reducing agent is supplied to the exhaust gas for this purpose.
Ammonia, for example, is used as a reducing agent. In particular,
in the case of exhaust-gas treatment devices for mobile internal
combustion engines, ammonia should not be stored directly but
rather in the form of a reducing agent precursor for safety
reasons. A reducing agent precursor of that type is, for example,
32.5% urea-water solution which can be converted to form ammonia
and which is available, for example, under the trademark "AdBlue."
However, the storage of a urea-water solution likewise leads to
problems because it freezes at temperatures below -11.degree. C. A
further known reducing agent precursor is Denoxium which remains
liquid even at temperatures below -11.degree. C. There is
nevertheless the same problem there, too, at lower temperatures.
Where the expression "reducing agent" is used below, it also means,
in particular, a reducing agent precursor and/or a reducing agent
precursor solution.
[0005] Specifically in the case of motor vehicles, temperatures
below -11.degree. C. may be encountered, for example, if the motor
vehicles have had long standstill periods between individual
operational phases. The tank and the delivery unit for the
urea-water solution must therefore be constructed so as to
withstand the freezing of reducing agent in the interior thereof
without being destroyed by the ice pressure which is generated. It
is thus advantageous for a return line to be provided for the
delivery unit. The return line may be closed off by a valve during
operation. In standstill situations, the ice pressure generated in
the delivery unit can be dissipated through the return line if the
valve is open then. At the same time, a closable return line
permits the discharge of air and/or gas bubbles and/or solid matter
(for example small fragments of ice) from the delivery unit and the
associated lines, such as may arise during the freezing or thawing
of the reducing agent in the interior of the delivery unit. In
order to ensure that the delivery unit can reliably provide (in
particular only liquid) reducing agent in an exactly predefined
quantity and/or at an exactly predefined pressure, it is important
for as few air bubbles as possible to be present in the delivery
unit and in the associated lines.
[0006] There is normally only a limited amount of electrical energy
available in a motor vehicle. For that reason, it is advantageous
if the delivery unit can be operated with little energy. In
particular, the closable valve in the return line constitutes an
energy consumer. In order to ensure that ice pressure can be
dissipated when the motor vehicle is at a standstill, the valve
must be opened. A valve must therefore be used which is open when
no supply voltage is applied. Conversely, for the operation of the
delivery unit, it is then necessary for an operating voltage to be
applied to the valve, and therefore for energy to be consumed.
SUMMARY OF THE INVENTION
[0007] It is accordingly an object of the invention to provide a
method for operating a delivery unit for a reducing agent and a
motor vehicle having a delivery unit, which overcome the
hereinafore-mentioned disadvantages and further alleviate the
highlighted technical problems of the heretofore-known units and
motor vehicles of this general type. It is sought, in particular,
to describe a method for particularly energy-saving operation of a
delivery unit which has an electrically activatable valve.
[0008] With the foregoing and other objects in view there is
provided, in accordance with the invention, a method for operating
a delivery unit for reducing agent. The delivery unit has a feed
line running from a tank to an addition point, a return line
branching off from the feed line, and a valve configured to be
activated with an electrical current for switching over the return
line. The method comprises at least the following steps: [0009] a)
applying an activation current to the valve for a first time
interval; [0010] b) applying a holding current to the valve when
the first time interval has elapsed; [0011] c) determining an
operating variable of the delivery unit; and [0012] d) adapting at
least one of the following variables as a function of the
determined operating variable: [0013] the activation current;
[0014] the holding current; [0015] the first time interval.
[0016] The method according to the invention is based on the
consideration that a lower operating voltage is required for
maintaining an activated position than for the transition from an
initial position into the activated position of the valve. In the
initial position, the valve is in each case either open or closed.
In the activated position, the respective other state (closed or
open) is then present. Within the context of the invention, a
switchover of the valve means that the valve is transferred either
from a closed state into an open state or from an open state into a
closed state. This is dependent on the type of valve. In order to
ensure that the transition into the activated position can take
place reliably, the higher operating voltage required for this
purpose (the activation current) must be applied for a certain
period of time (the first time period). Thereafter, a lower current
or a lower voltage for maintaining the activated position (the
holding current) can be applied, as an operating current, to the
valve. As an alternative to the activation current and the holding
current, it is also possible within the context of the present
invention for an activation voltage and a holding voltage to be
defined. Voltage and current are linked to one another by Ohm's
law, in such a way that the current is always approximately
proportional to the associated voltage. If appropriate, through the
use of a regulator, an adaptation of current and/or voltage may
take place in such a way that in each case a desired voltage or a
desired current is present.
[0017] With regard to the construction of the correspondingly
configured device, reference is made to the introduction and to the
explanations given below. It should be noted that the feed line
permits a transportation of (liquid) reducing agent away from the
tank (to a buffer storage device, an injector, a filter, a dosing
unit, an evaporator, a reaction chamber, a mixing chamber, etc.)
and the return line permits a transportation of the reducing agent
from a (single) point of the feed line back to the tank.
[0018] In order to carry out the electric operation of the valve, a
corresponding voltage or current source is provided, along with a
controller which effects corresponding operation of the valve. Even
though a single valve and/or a single return line is sufficient in
most cases, the invention may also be used correspondingly with a
multiplicity of valves and/or return lines.
[0019] In accordance with another particularly advantageous mode of
the method of the invention for operating the delivery unit, the
valve has a movable armature which can be moved from an initial
position into an activated position by the activation current and
can be held in the activated position by the holding current. If an
electrical voltage is applied to the valve, an electrical current
flows through an exciter coil provided in the valve. An exciter
coil of the valve thus generates a magnetic force, which acts on
the armature in the valve. The armature can be moved in this way.
The movable armature may, in particular, be a piston or a
diaphragm. It is also possible for both a piston and also a
diaphragm to be provided, and for a force and a movement to be
transmitted from the piston to the diaphragm through a transmission
fluid. Consequently, it is proposed herein, in particular, that the
exciter coil be activated through the use of the activation current
in such a way that the armature undergoes a change in position, and
is subsequently held stationary in the desired activated position
through the use of the holding current.
[0020] In accordance with a further mode of the method of the
invention, the valve has a movable armature, a spring and an
exciter coil, and the exciter coil can move the movable armature
counter to a spring force of the spring. A reactive element is thus
additionally provided in this case, which element counteracts the
force generated by the exciter coil and moves the armature of the
valve back into the initial position. The reactive element may, for
example, be a spring. When no operating voltage or too low an
operating voltage is applied to the valve, the reactive element
moves the armature back into the initial position. Through the use
of the exciter coil and the described reactive element together, it
is thus possible for the armature of the valve to be moved back and
forth between the initial position and the activated position.
[0021] The armature normally opens up or closes off a duct for a
medium. When the duct is opened up, the valve is open. When the
duct is closed off, the valve is closed.
[0022] It is desirable for the activation current to be as low as
possible and to have to be applied for as short a first time
interval as possible in order to move the armature of the valve
from the initial position into the activated position. Furthermore,
the holding current for maintaining the activated position should
be as low as possible. It is thus possible for the energy
consumption of the valve to be kept low.
[0023] An example for the procedure of the method is specified
herein, as an example for the method according to the
invention:
[0024] An activatable solenoid valve may be used as a valve. In
step a), an activation current of between 400 mA [milliamperes] and
1000 mA, preferably approximately 700 mA, can be applied to the
valve. The activation current is applied in step a) for a first
time interval of between 0.5 s [seconds] and 2 s, preferably
approximately 1 s. Subsequently, in step b), a holding current of
between 20 mA [milliamperes] and 500 mA, preferably between 200 mA
and 300 mA, is applied. If appropriate, the holding current is now
varied within step b). For example, the holding current is reduced
continuously (if appropriated in stages) in the manner of an
iteration (in particular stepwise or repeatedly). This can be done,
for example, in steps of 2 mA [milliamperes] to 20 mA in each case.
At the same time, in step c), it may be monitored as to whether or
not leakage of the valve occurs. If leakage of the valve occurs, a
minimum required holding current for preventing leakage is defined
in step d). The minimum required holding current may, for example,
be higher than the defined holding current by a predefined
difference of, for example, between 10 mA [milliamperes] and 50 mA.
The method according to the invention is subsequently started
anew.
[0025] Through the use of the method according to the invention,
the activation current, the holding current and/or the first time
interval can be adapted to relevant operating variables of the
delivery unit. It is possible for the activation current, the first
time interval and/or the holding current to be varied in such a way
that relevant operating variables of the delivery unit lie in an
acceptable range, so that fault-free operation of the delivery unit
is ensured and at the same time the energy consumption of the valve
is as low as possible.
[0026] In accordance with an added particularly advantageous mode
of the method of the invention, step c) takes place at least as a
function of a determined operating variable of the delivery unit,
wherein the operating variable includes at least one of the
following parameters: [0027] pressure of the reducing agent in the
delivery unit; [0028] delivery rate of a delivery pump assigned to
the delivery unit; [0029] characteristic current profile of a
delivery pump assigned to the delivery unit; [0030] leakage from
the delivery unit; [0031] temperature of the reducing agent in the
delivery unit; [0032] temperature of a component in the delivery
unit.
[0033] With this improvement of the method, it is achieved, in
particular, that monitoring or even diagnosis of at least some of
these operating variables of the delivery unit takes place, and the
operation of the delivery unit can be manipulated in a targeted
manner (directly and/or approximately simultaneously and/or in a
regulated manner) through the operation of the valve.
[0034] If the holding current, the activation current and/or the
first time interval are too low/short for the presently or actually
prevailing conditions, a sufficient pressure build-up in the
delivery unit is not possible because a pressure loss occurs
through the return line in parallel with the pressure build-up by
the pump. It is therefore advantageous for the holding current, the
activation current and/or the first time interval to be adapted to
the pressure in the delivery unit.
[0035] The delivery rate or the delivery volume of the delivery
unit is generally increased if the holding current, the activation
current and/or the first time interval are too low/short, because a
loss of delivery rate occurs through the return line. It is
therefore advantageous for the activation current, the holding
current and/or the first time interval to be increased if the
actual delivery rate is presently increased in relation to an
expected and/or predefined delivery rate. If the first time
interval is too short and/or the activation current is too low, the
switchover process of the valve into the activated state possibly
takes place incompletely. If the holding current is too low, the
valve is not held in the switched-over state after the
activation.
[0036] It is possible to infer the pressure build-up and/or the
delivery rate of a delivery pump from the characteristic current
profile of the delivery pump which is assigned to the delivery
unit. It is thus also possible for the activation current, the
holding current and/or the first time interval to be adapted
directly to the characteristic current profile of a delivery pump
of that type. A delivery pump of that type may be a
reciprocating-piston pump or a diaphragm pump with a pump chamber
and a movable pump piston. The piston is moved back and forth by an
electromagnetic coil. The characteristic current profile of a
delivery pump is generated when a predetermined voltage signal is
applied to the delivery pump. The voltage signal may be a
rectangular voltage signal. Alternatively, the voltage signal may,
like the voltage signal for the method according to the invention,
be divided into a plurality of chronological phases of different
voltage. It is possible, for example, for an acceleration voltage
for accelerating the pump piston and a (different) movement voltage
for moving the pump piston to be provided. It is possible to infer
the delivery rate of the pump and the pressure build-up in the
delivery unit from the characteristic current profile, through the
movement of the pump piston and the resistance of the medium in the
pump.
[0037] Both the pressure build-up in the delivery unit and also the
delivery rate of the pump are possibly also related to a (desired
or undesired) leakage from the delivery unit (including the
associated lines). The leakage is the cause for an increased
delivery rate of the delivery pump without correspondingly
increased transportation to the desired destination, and impaired
pressure build-up. One possible position for leakage is an
incompletely closed valve in the return line. An incompletely
closed valve may be the result of too low a holding current, too
low an activation current and/or too short a first time interval.
It is therefore expedient for the holding current, the activation
current and/or the first time interval to be adapted to a leakage
of the delivery unit and, in particular, to a leakage at the valve
in the return line.
[0038] If a leakage has been detected, the method according to the
invention should be started anew in order to ensure that, in
particular, step a) of the method is carried out anew. If leakage
occurs, the valve is not fully switched over. The holding current
which has been set too low is, however, not capable of moving the
valve into the fully switched-over state. For this reason, in step
a), the activation current which ensures a complete switchover of
the valve should be applied anew.
[0039] It is also advisable for the activation current, the holding
current and/or the first time interval to be adapted to a
temperature measured in the reducing agent and/or on a component of
the delivery unit. The electrical characteristics and, in
particular, the electrical resistance of a valve may be dependent
on the temperature, such that it is particularly advantageous for
the activation current, the holding current and/or the first time
interval to be adapted to a temperature of the valve or of a
component disposed in the vicinity of the valve. The viscosity of
the reducing agent is also at least partially dependent on the
temperature of the reducing agent. The holding currents, activation
currents or first time intervals required may change due to a
changed viscosity of the reducing agent. For example, an increased
viscosity may hinder the movement of the valve. It is therefore
advantageous for the activation current, the first time interval
and/or the holding current to be adapted to the temperature of the
reducing agent.
[0040] In accordance with an additional advantageous mode of the
method of the invention, the method is carried out repeatedly and
an adaptation of at least one of the following variables to an
aging-induced change of the valve is carried out: [0041] the
activation current; [0042] the holding current; [0043] the first
time interval.
[0044] Even though the adaptation could be carried out jointly
during the course of step c), it is preferable in this case for the
adaptation to be carried out not during every operation of the
valve but rather only at predefined points in time. Such points in
time may be a first start-up, servicing times, mileage limits,
etc.
[0045] An aging-induced change of the valve may, for example,
result in the effect of the valve on the delivery rate of the
delivery unit, and/or a leakage flow through the valve, being
increased. For example, the armature of the valve and/or the
contact area of the valve for the armature may change as a result
of operation, in such a way that a leakage flow through the valve
is generated. It is, however, possible for such wear of the valve
to be at least partially compensated for by an increased holding
current, in such a way that a leakage flow is prevented or at least
reduced to such an extent that fault-free operation of the delivery
unit can nevertheless be ensured. It is also possible that the
force imparted by a restoring element of the valve changes over
time. The restoring element may, for example, be a spring which
ages and eventually imparts a lower spring force. It is now
possible for the activation current, the first time interval and/or
the holding current to be reduced, and for fault-free operation of
the delivery unit to nevertheless be ensured.
[0046] In accordance with yet another likewise advantageous mode of
the invention, the method is carried out upon a first start-up of
the delivery unit, and an adaptation of at least one of the
following variables to individual characteristics of the valve
resulting from production tolerances is carried out: [0047] the
activation current; [0048] the holding current; [0049] the first
time interval.
[0050] Valves from a production series generally differ because
absolutely exact production is often not possible. It is possible
for such fluctuations in production quality to be utilized to
further reduce the energy consumption for a delivery unit. It may
be the case that, to hold the valve in the activated position in
different valves of the same type or of the same type series,
different holding currents are required. The activation currents
may also differ. This may, for example, result from the fact that
the spring force of a spring which pushes or pulls the armature of
the valve back into the initial position may vary. In this respect,
it is proposed herein that in fact the individual characteristics
of the valve be determined, and that specifications for the
adaptation of the operating variables be predefined specifically
for the individual valve.
[0051] With regard to the variation of the delivery unit as a
result of aging and with regard to the production tolerances, the
adaptation within the context of the method according to the
invention preferably takes place in a self-adapting manner. That is
to say, within the context of the adaptation, no individual
setting-up or programming of different delivery units takes place
from a production line, but rather the adaptation is carried out
substantially automatically. In particular, deviations of the
delivery units within the production tolerances during manufacture
are not monitored. The adaptation to differences of the delivery
units within the production tolerances takes place in a
self-adapting manner or automatically, without such monitoring
taking place. Variations due to aging are usually not even
detectable because the aging of the delivery unit occurs during
operation, and a renewed measurement of the delivery unit normally
does not take place during operation. It is therefore necessary, in
particular in the case of an adaptation due to aging, for the
adaptation to take place in a self-adapting manner or
automatically.
[0052] In accordance with yet a further particularly advantageous
mode of the method of the invention, in step b), the holding
current is reduced to such an extent that leakage from the delivery
unit is detected in step c), and then in step d), the holding
current is set so as to be higher by a predefined interval than the
holding current which was reduced in step b). The predefined
interval (in particular an interval of the voltage increase) should
be selected in such a way that the holding current set in step d)
ensures with sufficient certainty that no further leakage from the
delivery unit occurs thereafter. In this way, it is possible for
the energy demand of the valve for maintaining the activated
position of the valve to be reduced to a particularly great
extent.
[0053] In a further advantageous embodiment of the method, an
activation current is applied to the valve in step a), and in step
c) it is checked, through the use of one of the relevant
parameters, whether or not that activation current was sufficient
to actuate the valve. For example, it may be checked whether or not
a leakage flow through the valve is generated. In step d), the
activation current is then adapted correspondingly. If the valve
has been actuated as desired, the activation current is reduced
further. If the activation current was too low to actuate the
valve, the activation current is increased again by a predefined
suitable interval, in such a way that a successful activation of
the valve is ensured with adequate certainty. The method can also
be applied to the duration of the first time interval, wherein
through the use of a corresponding method implementation, the first
time interval can be selected to be particularly short.
[0054] In accordance with yet an added particularly advantageous
mode of the method of the invention, the activation current and the
holding current are generated from a system voltage through a pulse
width manipulation. In the on-board power system of the motor
vehicle, a voltage is normally available which fluctuates by a few
volts, which results, for example, from the power of a generator
connected to the internal combustion engine and from a battery
provided for storing electrical energy. However, for the activation
according to the invention of a valve in the delivery unit,
operation with very precise specifications for the respective
operating voltage is preferable. An exact voltage which is lower
than an initial voltage may be generated, for example, through
pulse width manipulation. Through the use of pulse width
manipulation, it is possible to generate different voltages using a
single electrical circuit. Two different operating voltages, the
activation current and the holding current, are required for the
method according to the invention. Therefore, pulse width
modulation is particularly well suited to the method proposed
herein.
[0055] In accordance with yet an additional advantageous mode of
the method of the invention, a free-wheeling diode is connected in
parallel with the activatable valve and a deactivation of the
holding current takes place after step d). During the deactivation
of a valve (in particular of a magnetically operated valve), the
electrical energy stored in the valve (or in the magnets of the
valve) flows back after the deactivation and generates a short
voltage peak which can lead to damage to electronic components.
That voltage peak can be successfully prevented through the
parallel connection of the valve with a free-wheeling diode or a
protective diode. In particular, if the method according to the
invention is carried out frequently and multiple times in rapid
succession, it is thus possible for disturbing influences of
preceding method cycles (steps a) to d)) to be effectively
eliminated.
[0056] With the objects of the invention in view, there is
concomitantly provided a motor vehicle, comprising an internal
combustion engine and an exhaust system for purification of exhaust
gases of the internal combustion engine. The motor vehicle has a
delivery unit with a feed line which runs from a tank to an
addition point and a return line which branches off from the feed
line. The return line can be closed off by a valve which can be
activated with an electrical voltage. The motor vehicle has a
controller which is set up, configured or programmed for operating
the delivery unit in accordance with a method of the invention.
[0057] The controller may also be jointly integrated into the
engine controller of the motor vehicle, so that a separate
component need not be provided for the control of the delivery
unit. The method may, for example, be integrated as software into
the controller. The controller may furthermore interact with
suitable (calculated and/or stored) data models, sensors, etc., in
order to perform an up-to-date adjustment or adaptation of the
operation of the valve.
[0058] Other features which are considered as characteristic for
the invention are set forth in the appended claims, noting that the
features specified individually in the claims may be combined with
one another in any desired technologically meaningful way and may
be supplemented by explanatory facts from the description, with
further structural variants of the invention being specified.
[0059] Although the invention is illustrated and described herein
as embodied in a method for operating a delivery unit for a
reducing agent and a motor vehicle having a delivery unit, it is
nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein
without departing from the spirit of the invention and within the
scope and range of equivalents of the claims.
[0060] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0061] FIG. 1 is a diagrammatic, vertical-sectional view of a
delivery unit configured for performing the method according to the
invention;
[0062] FIG. 2 is a longitudinal-sectional view of a valve which may
be disposed in a delivery unit and through which the method
according to the invention can be carried out;
[0063] FIG. 3 is a further longitudinal-sectional view of the valve
of FIG. 2;
[0064] FIG. 4 is a graph of a voltage profile generated through
pulse width modulation;
[0065] FIG. 5 is a flow diagram of the method according to the
invention; and
[0066] FIG. 6 is a sectional view of a motor vehicle having a
delivery unit.
DETAILED DESCRIPTION OF THE INVENTION
[0067] Referring now to the figures of the drawings in detail and
first, particularly, to FIG. 1 thereof, there is seen a delivery
unit 2 (or a complete dosing unit with an injector into an exhaust
system 17) for a liquid reducing agent such as, for example, a
urea-water solution. The delivery unit 2 delivers reducing agent
from a tank 3 to an addition or metering-in point 4. The reducing
agent is delivered from the tank 3 to the addition point 4 through
a feed line 5. A filter 19 and a delivery pump 13 are disposed in
the feed line 5, as seen in a flow direction of the reducing agent.
A single return line 6 branches off from the feed line 5 downstream
of the filter 19 and the delivery pump 13, as viewed from the tank
3. The return line 6 can be closed off through the use of an
electrically operable valve 1. A pressure sensor 20 and a
temperature sensor 21 are situated in the feed line 5 between the
delivery pump 13 and the addition point 4. The pressure sensor 20
and the temperature sensor 21 may be realized either separately
from one another or in a common structural unit. The addition point
4 is set up or configured to dose reducing agent in predefined, if
appropriate variable quantities into the exhaust system 17.
[0068] The method according to the invention is carried out by a
controller 18. The controller is connected to the delivery pump 13,
the pressure sensor 20, the temperature sensor 21 and the addition
point 4, in order to process information or signals generated by
those components and to define therefrom an activation current, a
holding current and a first time interval for the valve 1, which is
likewise connected to the controller 18.
[0069] FIG. 2 and FIG. 3 show an example of a valve 1 which can be
used in a delivery unit for the method according to the invention.
FIG. 2 shows the valve 1 in an initial position 29, and FIG. 3
shows the valve 1 in an activated position 30. In the initial
position 29, a connection from an inlet duct 23 leading into the
valve 1 to an outlet duct 24 leading out of the valve 1 is closed
off. The reducing agent cannot flow from the inlet duct 23 through
the valve 1 to the outlet duct 24. In the activated position 30,
the connection from the inlet duct 23 leading into the valve 1 to
the outlet duct 24 leading out of the valve 1 is open. The reducing
agent can now flow from the inlet duct 23 through the valve 1 to
the outlet duct 24. A movable armature 10 in each case closes and
opens the connection from the inlet duct 23 to the outlet duct 24.
The armature 10 is held in the initial position 29 through the use
of a spring 12. The armature 10 can be moved counter to the force
exerted by the spring 12 by an exciter coil 11, in such a way that
the valve 1 can be transferred into the activated position 30. The
exciter coil 11 is supplied with electrical energy by a voltage
source 22. Additionally, FIG. 3 shows a free wheeling diode 32 in
parallel with the activatable valve.
[0070] FIG. 4 diagrammatically illustrates how an activation
voltage 7 and/or a holding voltage 9 can be generated from a
present system voltage 14 by pulse width manipulation. In
accordance with Ohm's law, the holding current is determined from
the holding voltage 9, and the activation current is determined
from the activation voltage 7, on the basis of the electrical
resistance of the valve and of the other connected components. If
appropriate, an adaptation of the activation voltage 7 and of the
holding voltage 9 through regulation may take place, in which the
activation voltage 7 and the holding voltage 9 are adapted in such
a way that the desired activation current and the desired holding
current are set exactly. In FIG. 4, a voltage profile over time is
plotted on a voltage axis 28 against a time axis 27. Within the
context of the pulse width modulation, a fixed pulse width 25 is
predefined within which the system voltage 14 is pulsed with a
variable pulse length 26. The pulsed system voltage 14 is applied
to an electrical circuit set up for pulse width modulation. A
fluctuating system voltage 14 may be compensated for through an
adaptation of the pulse length 26. A correspondingly reduced
voltage is attained at the output of the circuit as a function of
the predefined pulse length 26. In the case of the method according
to the invention discussed herein, that voltage is either the
activation voltage 7 or the lower holding voltage 9. The activation
voltage 7 is generated for a first time interval 8 for the method
according to the invention. From then onward, the pulse length 26
is reduced, and the holding voltage 9 is generated.
[0071] FIG. 5 shows a flow diagram of a preferred variant of the
method according to the invention. Individual method steps a), b),
c) and d) are run through repeatedly in the form of a loop. In
particular, in the case of a method implementation of the method
according to the invention, in which the activation current, the
holding current and the first time interval are reduced to the
greatest possible extent, in each case one control run-through 31
is possible upon the conclusion of the method according to the
invention. During the course of that control run-through 31, no
further adaptation of the activation current, of the holding
current and of the first time interval takes place, but rather it
is merely checked whether or not the operating parameters of the
delivery unit with the present activation current, the present
holding current and the present first time interval lie in the
desired range. Step d) is accordingly omitted in the concluding
control run-through.
[0072] FIG. 6 shows a motor vehicle 15 having an internal
combustion engine 16 and an exhaust system 17. The exhaust system
17 can be supplied with reducing agent from a delivery unit 2
through an addition point 4. The delivery unit 2 is a delivery unit
which can be operated through the method according to the
invention.
[0073] It is basically pointed out herein that the method may also
be used correspondingly for other additives for motor vehicles
which can be delivered through the use of a corresponding delivery
unit with a feed line and a return line connectable by an
electrically operable valve. Such (fluid) additives include, in
particular, fuel, oxidation media or agents and the like. The
addition point may, for this purpose, be relocated to addition
points suitable for the additives, such as for example an intake
region of the internal combustion engine or, in a targeted manner,
upstream/downstream of an exhaust-gas treatment unit (filter,
catalytic converter, mixer, etc.).
* * * * *